Ferristatin II Promotes Degradation of Transferrin Receptor-1 In Vitro and In Vivo

Previous studies have shown that the small molecule iron transport inhibitor ferristatin (NSC30611) acts by down-regulating transferrin receptor-1 (TfR1) via receptor degradation. In this investigation, we show that another small molecule, ferristatin II (NSC8679), acts in a similar manner to degrade the receptor through a nystatin-sensitive lipid raft pathway. Structural domains of the receptor necessary for interactions with the clathrin pathway do not appear to be necessary for ferristatin II induced degradation of TfR1. While TfR1 constitutively traffics through clathrin-mediated endocytosis, with or without ligand, the presence of Tf blocked ferristatin II induced degradation of TfR1. This effect of Tf was lost in a ligand binding receptor mutant G647A TfR1, suggesting that Tf binding to its receptor interferes with the drug’s activity. Rats treated with ferristatin II have lower TfR1 in liver. These effects are associated with reduced intestinal 59Fe uptake, lower serum iron and transferrin saturation, but no change in liver non-heme iron stores. The observed hypoferremia promoted by degradation of TfR1 by ferristatin II appears to be due to induced hepcidin gene expression

Iron-Responsive Olfactory Uptake of Manganese Improves Motor Function Deficits Associated with Iron Deficiency

Iron-responsive manganese uptake is increased in iron-deficient rats, suggesting that toxicity related to manganese exposure could be modified by iron status. To explore possible interactions, the distribution of intranasally-instilled manganese in control and iron-deficient rat brain was characterized by quantitative image analysis using T1-weighted magnetic resonance imaging (MRI). Manganese accumulation in the brain of iron-deficient rats was doubled after intranasal administration of MnCl2 for 1- or 3-week. Enhanced manganese level was observed in specific brain regions of iron-deficient rats, including the striatum, hippocampus, and prefrontal cortex. Iron-deficient rats spent reduced time on a standard accelerating rotarod bar before falling and with lower peak speed compared to controls; unexpectedly, these measures of motor function significantly improved in iron-deficient rats intranasally-instilled with MnCl2. Although tissue dopamine concentrations were similar in the striatum, dopamine transporter (DAT) and dopamine receptor D1 (D1R) levels were reduced and dopamine receptor D2 (D2R) levels were increased in manganese-instilled rats, suggesting that manganese-induced changes in post-synaptic dopaminergic signaling contribute to the compensatory effect. Enhanced olfactory manganese uptake during iron deficiency appears to be a programmed “rescue response” with beneficial influence on motor impairment due to low iron status

Determination of grain boundary volume expansion by HREM

High resolution electron microscopy (HREM) has provided invaluable insight into the structure of grain boundaries at the atomistic level. Quantitative HREM methods are now in development which, combined with atomistic simulations, can provide further insight into grain boundary structure-energy correlations. For example, the volume expansion (or excess free volume, {delta}), a thermodynamic parameter directly related to the grain boundary energy, is represented by the normal component of the rigid body translation. Although its magnitude is small, it can be determined experimentally using statistical techniques which locate and fit the peak and valley positions in an experimental HREM image - i.e., a direct measurement of the lattice fringe displacements is made. We have modified the lattice fringe displacement technique such that a measurement accuracy of better than {plus_minus}0.002a{sub o} can be achieved. Precise knowledge of the position and intensity of the image contrast and a detailed understanding of the sources of error are required. This paper provides a detailed description of the lattice fringe displacement technique as well as an analysis of the sources of error in the measurement

Atomic structure of heterophase interfaces

High-resolution electron microscopy (HREM) has been used to study internal interfaces between dissimilar materials, notably ceramic/metal interfaces. Structures observed for system with small and large misfits are compared in metal/metal, metal/ceramic, and ceramic/ceramic boundaries. The interfaces were prepared by a variety of techniques, including internal reduction, internal oxidation, and epitaxial growth by MOCVD and special thin-film techniques. While interfaces produced by internal oxidation and reduction in fcc systems typically form boundaries on (111) planes, non-equilibrium boundaries have also been generated using special thin film techniques. All boundaries can be characterized by their tendency to form coherent structures. While it appears that the amount of misfit and the bond strength primarily determine the degree of coherency, kinetic factors and substrate defects also seem to play an important role in determining the local defect structure at the boundary and the type of misfit localization. 24 refs., 9 figs., 1 tab

Evidence that diacylglycerol acyltransferase 1 (DGAT1) has dual membrane topology in the endoplasmic reticulum of HepG2 cells

Triacylglycerol (TAG) synthesis and secretion are important functions of the liver which have major impacts on health, as over-accumulation of TAG within the liver (steatosis) or hypersecretion of TAG within very-low-density lipoproteins (VLDL) both have deleterious metabolic consequences. Two diacylglycerol acyltransferases (DGATs 1 and 2) can catalyse the final step in the synthesis of TAG from diacylglycerol (DAG) which has been suggested to play an important role in the transfer of the glyceride moiety across the endoplasmic reticular membrane for (re)synthesis of TAG on the lumenal aspect of the endoplasmic reticular (ER) membrane [Owen, M., Corstorphine, C.G., and V.A. Zammit (1997) Biochem. J. 323, 17-21 ]. Recent topographical studies suggested that the oligomeric enzyme DGAT1 is exclusively lumen-facing (latent) in the ER membrane. By contrast, in the present study, using two specific inhibitors of human DGAT1, we present evidence that DGAT1 has a dual topology within the ER of HepG2 cells, with approximately equal DGAT1 activities exposed on the cytosolic and lumenal aspects of the ER membrane. This was confirmed by the observation of the loss of both overt (partial) and latent (total) DGAT activity in microsomes prepared from livers of Dgat1 -/- mice. Conformational differences between DGAT1 molecules having the different topologies were indicated by the markedly different sensitivities of the overt DGAT1 to one of the inhibitors. These data suggest that DGAT1 belongs to the family of oligomeric membrane proteins that adopt a dual membrane topology

Comparisons of observed and simulated atomic structures of Pd/NiO heterophase interfaces

High-resolution electron microscopy (HREM) and image simulation using the multislice algorithm were used to study the atomic structure of a Pd/NiO (111) interface in an internally oxidized sample. These samples have cube-on-cube oriented or twin-related precipitates whose (111) interfaces exhibit a contrast modulation along the boundary plane in the HREM image. Previous studies have reported that the observed structural period of this modulation corresponds qualitatively to the expected spacing if the boundary were composed of a network of misfit dislocations. In this study, rigid models of the (111) interface as viewed from the [110] direction were simulated using the EMS suite of programs. The questions addressed are whether the terminating plane on the oxide side is made up of a Ni or an O layer, and whether a rigid body translation normal to the interface exists. Results of simulations are compared and contrasted to through-focal experimental images to investigate the origin of the contrast modulations and their possible relation to the extent of the misfit localization in these systems. 6 figs, 1 tab, 11 refs